linux-kernel - RE: nic enumeration

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Message-ID: <D3F292ADF945FB49B35E96C94C2061B90C317F5F@nsmail.netscout.com>
Date:	Thu, 8 Jul 2010 18:07:24 -0400
From:	"Loke, Chetan" <Chetan.Loke@...scout.com>
To:	"Kay Sievers" <kay.sievers@...y.org>,
	"Andrew Fong" <ayf@...tube.com>
Cc:	"Matt Domsch" <Matt_Domsch@...l.com>,
	"Michael Di Domenico" <mdidomenico4@...il.com>,
	<linux-net@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: nic enumeration

> -----Original Message-----
> From: Kay Sievers [mailto:kay.sievers@...y.org]
> Sent: July 08, 2010 5:28 PM
> To: Andrew Fong
> Cc: Loke, Chetan; Matt Domsch; Michael Di Domenico; linux-
> net@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: nic enumeration
> 
> On Thu, Jul 8, 2010 at 22:47, Andrew Fong <ayf@...tube.com> wrote:
> > On Thu, Jul 8, 2010 at 1:36 PM, Loke, Chetan
> <Chetan.Loke@...scout.com> wrote:
> >>> -----Original Message-----
> >>> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
> >>> owner@...r.kernel.org] On Behalf Of Matt Domsch
> >>> Sent: July 07, 2010 9:21 PM
> >>>
> >>> http://lwn.net/Articles/356900/
> >>>
> >>> And on a system where you can use udev rules, the
> >>> 70-persistent-net.rules file can be used to make them constant, by
> >>> using the MAC address to force the names to be what you want.
> >>
> >> Ok, but can we achieve the renaming w/o a reboot?
> >
> > You probably can restart the udev subsystem.
> 

> No, udev has not really a concept of being restarted, it will not do
> anything. You can only synthesize events, so it looks like the device
> is just plugged in. For that, you need to make sure the interface is
> not busy, otherwise renaming will fail in interesting ways, especially
> if names need to be swapped between several devices.
> 

I'm not a udev guru so I don't know how will renaming a simple net_device->name work?
What about the msi-x queues created by the driver? May be I missed it but I don't see a single driver tearing apart everything and restarting unless a NETDEV_RENAME somehow automagically reloads the driver. I know it's silly for the driver to tear apart the whole world. But then why allow renaming in the first place, correct?

> Live renaming of interfaces is something you really need to know what
> you are doing, especially on remote machines.
> 

I agree, I wanted someone to say 'try the symlink attrib'. I really need to create a 'symlink' or a reference to the newly added 'ethX' interface. I have to support 75+ VMs(each w/ 5+ vNICs) and I can't [re]name the newly added vNIC and then reboot. Rebooting 75+ VMs is non-practical. Adding a new vNIC is as simple as point-and-click and the guest sees the new vNIC. The VM doesn't need to reboot.

How do I achieve this 'symlinking' effect minus the reboot?

> Kay

Regards
Chetan Loke